One of the most readily identified features on a landscape, streams are generally understood to be linear bodies of water with a current that is the result of gravity. A basic understanding of stream structure and function is fundamental to conservation, restoration, and monitoring activities. Streams and stream channels are dynamic, constantly changing in response to both natural and human-induced disturbances including weather conditions and land-use activities within the watershed. These systems function within ranges of temperature, flow, sediment, and other variables, continually seeking a balance in a process called dynamic equilibrium. The ways in which stream systems adjust to achieve and maintain equilibrium will be described throughout this section.

Because of the water flow in stream channels for at least a portion of the year, lands in proximity to streams are characterized by distinctive soils and unique assemblages of plants and animals. These unique and botanically rich areas are termed riparian zones and serve many important functions within ecosystems:

• Provide habitat for many species of plants and wildlife
• Cycle nutrients
• Filter contaminants from runoff water before it reaches the stream channel
• Help control floodwaters
• Maintain streamflow
• Protect streambanks
• Build up stream banks by trapping sediment from flood waters

Streams also play the important role of transporting sediment within the watershed.

Streams and stream processes can be explored from three different perspectives:

• Longitudinal
• Lateral
• Temporal

We will use this framework to increase our understanding of these important features on our landscapes.